Stabilization of borax supersaturation in solutions



Dec. 11, 1956 STABILIZATION OF BORAX SUPERSATURATION IN SOLUTIONS D. s.TAYLOR ET AL 2,774,070

Filed April 10, 1955 SYMBOL s x F250,, 0 7H 0 O F2504 4): 4 20 0 F8504 Q4.2 H20 138$. BORAX CRYSTALL/ZED F ea/w 1001.86. SOLUTION nv 24 Homes .Q

0 e\ 0.05 am 0.15 0.20 W7. JOE'QCENT 1 2 o- Dev INGREDIENTS DONALD 5.Yin L02,

050265 A. CONNELL, JNVENTORS.

Arroeusys.

United States Patent sr-ABmI'zA'rIoN or BORAXSUPERSATURATION-INSOLUTIONS invention has to do generally with thestabilizationofsolutions that are supersaturated 'with respect to borax.

The: phenomenon of supersaturation is: particularly common in thegeneral system NazOB2OsH2O, with oriwithout other solutesr A metastablestate of supersaturation is frequently encountered; in which anexcessof: boratez-will stayin solution almost: indefinitely- 1n= theabsencezof appropriate.seedicrystals. InJsome 'caseseven in the presenceofseedscrystals the supersaturation is=quite persistent, and breaksrelatively slowly;

It has been discovered that certain substances, when present insolutions supersaturated with'trespect to borax, have a strong tendencyto stabilize the state of supersaturation. Such stabilizing agentspermit a more extreme degree ofsupersaturationto be effectively attainedand utilized, other conditions being the same;,and they maycxtend almostindefinitely a condition of supersaturation -that would otherwise be'relatively short lived.

The most marked effect, and in many respects the most frequently useful,is the change that such agents produce in.the behavior ofmoderately'supersaturated solutions in the. presence of. seed. crystals.In: many. instances: growth or"; seed crystals insuch. solutions issubstantially com-. pletely inhibited, even at concentrations that wouldnor mally produce fairly rapid precipitation.

The substances that have been found to have this remarkable property ofstabilizing solutions that are supersaturated with respect to boraxinclude ferric iron, which is most readily introducedinto solutions ofborates by dissolving a ferrous salt' and'providing in: the. solutionxanoxidizing agent'capable of oxidizing the ferrous ion to ferric ion.Under many practical conditions dissolved atmospheric oxygenisaneffective oxidizing agent; Or anysuitable oxidizing agent may beadded, such;.for example, as potassium dichromate, potassiumpermanganate and the like. The ferric iron may be in thezform of freeferric ion, or combined as ferric hydroxide, depending primarily uponthe pH of the solution. Atrelatively high: pH. thesolubility of ferric.hydroxide. is: extremely low in absence of'other. solutes, and isquite;low even-in concentrated solutions of borates. Considerablestabilization is still obtained under those conditions, and is probablycaused primarily either by the small concentration of. ferric hydroxidein solution or by the very fine ferric hydroxide precipitate.-

Aluminum, cupric, chromic and, to a lesser extent, zinc, calcium andmagnesium ions also act as stabilizing agents for excess borax insolution.

In addition to .the inorganic substances mentioned,

anionic organic substances having surface active propertieshave beenfound to be effective stabilizing agents. Such surface activesubstancesare described and claimed in our copending patent application, SerialNo. 117,806, filed September 26, 1949, now Patent 2,662,810, of whichthe present application is a continuation in part. Y

An example of the practical utilization of the. invention is provided bythe problem of. preparing solutions of sobility curve is. one

2,774,070 Par-tented Dec. 11, 19.56

water is consumed-andlessbulk ofsolution needs to be handled.

That procedure 1 is particularly useful Whenthe borate composition isof" the type describe'd-and claimed the" copendin'g patent applicationof George A. Gonn'ellen-' titled Supersaturated Borax Solutions and"Methods and Compositionsfor- Producing Same," Serial'No. 117,878;filedESe tember ZG; 1949,.nowPatent 2,643,947.. A's-is there: described.in .full. detail, .it has been discoveredthat a. mixture: of sodium;tetra'borate and-'boric acid (orsodium pentaborate) havingza.suitable-value of the molar ratioof- NazO/BEzQacan hedissolved directlyin-water to yield a: supersaturated solution. The; concentration-obtainable may be equal to or greater than the maximum of the pentaboratepeak of the normal solubility curve, which occurs typically at a valueof the sodium to boron ratio of from about 0.15 to about 0.25, dependingupon conditions such as temperature and presence of other solutes.

Animportant feature of that discovery is that the actual sodium to boronratio of the ingredients dissolved (and of the resulting solution) neednot coincide with the ratio at the peak of the solubility curve, but canbe considerably higher, and the concentration of the resulting solutionmay still be equal to or greater than that at the maximunrof the curve.Such direct solution of sodium tetrahorate to produce a supersaturatedsolution can be obtainedby using tetraborate containing five mols ofwater of hydration or less.

Anadva'nt'age of 'that' discovery in' preparing such solut-ions'-'forweed control purposes is that thevariation with temperature of thesodium to" boron ratio at which the soli1bility peak occurs can' belargely neglected. A dry composition of the typedescribed suitable forsolution-in water at onetemperature can thus be dissolved directly tothesame-concentration even in considerably colder water. Under the latterconditions a supersaturated solution ordinarily results. The practicaladvantage of being able' to stabilize that supersaturation byaddition'of a simple and relatively inexpensive stabilizing agent inaccordance with the presentinvention'is-obvious:

The; amount of any particular stabilizing agent that shouldv be. used'in auygiven instancedepends upon the conditions. of use, for-examplethe length of time that supersaturation. must be effectively-maintained;and dependsparticularlyupon th'e -degree of the supersaturation; Thelatter factoris' difilcult to define usefully in precise terms,- becauseof. the-wide'variation of the normal solubility' asafunctionofithe'ratio of NazOs to BzO'sin the solution.- Because" ofthe. natureof thatvariation, the tendency of borax: to: crystallizefromasupersaturated so'- lution depends: not only" upon the percentage excessof B203 in solution, but also upon' the: value of the ratio- NazO/BzOaand. the: behavio 'of' the solubility curve in that region. The-pentaborat'e.peak of the normal soluexample of such. rapid variation ofsolubility with variation of the NazO/BzOa ratio.

Many of the agents mentioned exhibit a veryconsiderable stabilizingeffect. when used in. a concentration of. 0.1 to 1% onthe dry weight ofthe other solutes prese ent. Insome instances, and undersome conditions;as

desired degree of stabilization.

A group of typical stabilizing efiects, obtained under uniformconditions tobe described, are illustrated acid and calcined borax only,in proportions to give respective sodium to boron ratios of 0.250 and0.253.- Solutions D (Table 2) were made up with a uniform quantity ofcalcined borax only, and had a ratio of 0.5.

which Solutions B and Cwere prepared comprised boric graphically in theaccompanying drawing. The solutions 5 In Table 1 the degree ofstabilization produced by the were made up by dissolving 1.5 lbs. of :adry mix per various additives may be judged either from the relativegallon of water, together with the indicated ferrous salt, decrease ofB203 concentration during 24 hrs. of conat C., yielding in everyinstance a solution supertinuous agitation, as compared to thecorresponding de-' saturated with respect to borax. The dry mixcomprised crease for solutions 1 and 4 without additives; or from 27.8%of NaClOs (an auxiliary weed killing agent) and '10 a. similarcomparison of the amount of borax crystallizing 72.2% of boric acid andcalcined borax in proportions out of solution during that period. Theshift in to give a molar ratio NazO/BzOa of 0.252. In all in- NazO/BzOaratio is directly attributable to the removal stances ferric iron wasprovided by supplying the indifrom the solution of a solute (borax)having a higher cated type of ferrous salt and allowing dissolvedatmosratio than the solution. It will be noted that solution phericoxygen to oxidize the ferrous iron to ferric. The 3 was completelystabilized, under theparticular experiamount of ferrous ion provided isshown as abscissa in mental conditions described. terms of percent onthe total of other solutes. Each In absence of stabilizing agentssolution 6 in Table solution was continuously agitated at 10 C., and theso 2 reached a state of equilibrium after 24. hrs. Therefore lutionphase was analyzed at 1 hr. and at 24 hrs. The the concentration ofB203, determined after that time, ordinates in the drawing represent theamount of borax represents the normal solubility at a sodium to boronthat crystallized out of solution between those two ratio of 0.5. Thatvalue of the normal solubility proanalyses, expressed in pounds per 100lbs. of solution. vides a base from which thedegree of stabilizationpro- The two points at the extreme left of the figure repreduced by theiron and aluminum may be judged.v The sent solutions to which nostabilizing agent'was added. concentration of B203 after 24 hrs. in thePresence of From those'solutions 2.5 lbs. borax crystallized out per 25the stabilizing agent was more than 25% greater than 100 lbs. ofsolution during 24 hrs. of continuous agitation the normal solubility ata NazO/BzOs ratio of 0.5. at 10 C. Although that amount ofcrystallization did Tables 1 and 2 follow. I

Table l Additive Percent NaaO/BzOa B20: Borax crystallized No. Solutlon24hrs., 1 Percent lb./l00 lb. Type on dry 1hr. 24 hr. 1hr. 24 hrsolution 5 mix A None 5. 03 5.61 23s .220 0.00 A Alz(SO4)s.l8HzO 0.745.83 5. 73 235 .227 0.37 A 01130451120 0.74 5. s0 5 0 230 .230 0.00 BNone 8.18 7 05 251 .242 0. 74 o Chromlc Chl0ride 0. 74 8.35 8.30 25'.250 0.18

not necessarily remove all supersaturation from the Table II lutions, itis .sufiicient to seriously interfere with use of 45 such solutions.Moreover, it provides a rough indica- I Additive tron of the degree ofsupersaturation existlngnn the s o- No solution 282 23; lutions asoriginally prepared. The progressive stabili- Percent 24 hrs. 7 zationof that supersaturation as more iron was provided y in the solution isclearly shown by the progressively de- 0 h creasing amount of boraxcrystallized out. When more D None 1 14- than 0.15%.ferrous ion(computed on the dry weight 1) Amati "5:0" 1:45 of the other solutes)was added, in the presence of an. D FecltzHgom-r 25 oxidizing agent(air), complete stabilization was obtained, and no crystallization ofborax was observed unw claim: 7 der the Particular experifnentalconditions employed- It 1. The method of stabilizing a state ofsupersaturation is E from the the detalled Source of" with respect toborax in aqueous solution during a hold is of P Importance Fompflred tothe "ing period of appreciable duration; said method com-' availableconcentration. The results given in the drawprising Producing an aqueoussolution that i b g W111 Serve as a gulda 111 determming the amount oftially saturated with respect to borax, providing in the iron thatshould be provided under other conditions. In l i a stabilizing agentselected from the group cOngeneral, as the pH of the solution increases,and as the sisting of ferric, cupric and chromic salts, the concerttemperature decreases, the effectiveness of ferric iron as n i f said ii i agent being greater than about a Stabilizer becomes less marked, P plargely one tenth percent on' the dry weight of the other solutes causeof the reduced Solubilityv 0f ferric hydfoxidepresent, and then holdingthe'solution continuously dur- Tables 1 and 2 give typical data 011Stabilizing effects ing the said holding period under conditions forwhich Obtained with certain agents other than iron, all at theequilibrium solubility with respect to borax is less C. In Table 1 thelast column gives the amount of borax than the existing boraxconcentration of the solution .by crystallizing from each solution,determined as just dean amount that is insufiicient, by virtue of thepresence scribed for the solutions represented in the drawingof the saidstabilizing agent, to cause appreciable crystal Solutions indicated assolution A were made with the lization of borax. 1 same dry mix justdescribed, except that the molar ratio 2. The method defined in claim ,1and in which the NazO/BzOa was:0.240',at the same dosage of 1.5 lbs. ofsaid stabilizing agent is a ferric salt. 7 dry mix per gallon of water.The compositions from 3. ,The method defined in claim 1 and in whichthe.

said stabilizing agent is a cupric salt.

4. The method defined in claim 1 and in which the said stabilizing agentis a chromic salt.

5. The method of stabilizing a state of supersaturation With respect toborax in aqueous solution during a holding period of appreciableduration; said method comprising producing an aqueous solution that issubstantially saturated with respect to borax, providing in the solutiona ferrous salt and an oxidizing agent capable of oxidizing the ferrousion to ferric form, and then holding the solution continuously duringthe said holding period under conditions for which the equilibriumsolubility With respect to borax is less than the existing boraxconcentration of the solution by an amount that is insufiicient, byvirtue of the presence of the dissolved ferric ion, to cause appreciablecrystallization of borax.

References Cited in the file of this patent UNITED STATES PATENTS1,812,347 Kuhnert June 30, 1931 2,089,557 Jacobi Aug. 10, 1937 2,662,810Taylor et a1 Dec. 15, 1953 OTHER REFERENCES Teeple: The IndustrialDevelopment of Searles Lake Brines, ACS Monograph Series No. 49 (1929),page 18. Published by Chemical Catalog Co, Inc., New York City.

1. THE METHOD OF STABILIZING A STATE OF SUPERSATURATION WITH RESPECT TOBORAX IN AQUEOUS SOLUTION DURING A HOLDING PERIOD OF APPRECIABLEDURATION; SAID METHOD COMPRISING PRODUCING AN AQUEOUS SOLUTION THAT ISSUBSTANTIALLY SATURATED WITH RESPECT TO BORAX, PROVINDING IN THESOLUTION A STABILIZING AGENT SELECTED FROM THE GROUP CONSISTING OFFERRIC, CUPRIC AND CHROMIC SALTS, THE CONCENTRATION OF SAID STABILIZINGAGENT BEING GREATER THAN ABOUT ONE TENTH PERCENT ON THE DRY WEIGHT OFTHE OTHER SOLUTES PRESENT, AND THEN HOLDING THE SOLUTION CONTINUOUSLYDURING THE SAID HOLDING PERIOD UNDER CONDITIONS FOR WHICH THEEQUILIBRIUM SOLUBILITY WITH RESPECT TO BORAX IS LESS THAN THE EXISTINGBORAX CONCENTRATION OF THE SOLUTION BY AN AMOUNT THAT IS INSUFFICIENT,BY VIRTURE OF THE PRESENCE OF THE SAID STABILZING AGENT, TO CAUSEAPPRECIABLE CRYSTALLIZATION OF BORAX.